Lifter Tapping?
 

Car: 1989 260E

I just returned from a trip for the weekend. While leaving the airport parking garage, I noticed a tapping noise up front, identical to what I would sometimes hear for 2 or 3 seconds after starting the car in cold weather. This time, however, the tapping does not stop. The sound precisely varies in volume and frequency with engine speed, and it visually matches the frequency of rocker arm movement, as I observed when I removed the oil filler cap and looked inside.

Looking under the hood, the noise is definitely from the front of the engine, and definitely a continuation of the tapping I mentioned upon cold weather starting. I checked the belt tensioner shock and that is not the culprit. I pulled the first three (front) spark plug wires in sequence and the tapping persists. Also, the car shakes noticeably, as if one cylinder is misfiring, and the oil pressure indicator needle is very active -- moving is a somewhat erratic manner.

The only work/additions to the engine in the past few weeks were: 1.) New injector seals 2.) Lucas Oil additive to engine (I detect a possible connection there).

The low oil light did come on briefly a few days ago, and I added about 2 quarts then, but upon checking the level am coming up a bit short and have since added 2 more.

If I reove the valve cover and have a look, would any problem area be obvious? I am scheduled to go to the mechanic's on Wednesday morning, and don't want to mess with anything unnecessarily.

Any thoughts or suggestions would be appreciated.

Removing the cover, given what has already been done, would sound like a good move.
I'd check for looseness in a rocker arm, and if you find a loose one, look around that arm carefully to see if maybe one of the cup-shaped "buttons" that go directly on top of the valve stem maybe flipped out of place and is laying around on top of the head. Seen this once before. Could also be a collapsed hydraulic compensator.

Gilly

Thanks Gilly.

Is it something I can correct, or should I wait a day and let the mechanic have a look? (Because it is an engine issue, I am inclined to err on the side of caution and look, but not touch.)

Based on its past behavior, and after reading the threads here, it sounds very much like a lifter, but who can be sure?

What's a hydraulic compensator? Is that another term for hydraulic lifter?

It wouldn't be that big of a deal to reinstall the small cup shaped spacer if that's what you find wrong. In the case I stated, I just reinstalled it and never had the problem again-it was a regular customer.
Maybe the valve stuck in place from sitting just long enough for this to happen-no real firm evidence of why it came out.

Yes, the hydraulic compensator you could think of as being a "lifter", although this term is usually thought of as being a pushrod engine part. Usually the lifter slides along the camshaft. On this engine the rocker arm has a polished curved section that rides on the camshaft, and the compensator is on the other end of the rocker over the valve stem. Keeping the valve lash in spec is the job of either of these parts.

A recommended procedure for checking for a collapsed compensator is to push down on the rocker arm on the side opposite the camshaft (the end of the rocker that the compensator is) and push down with something like a hammer handle and see if the rocker seems to move down alot.
But check just for alot of looseness first, to see if maybe it's just the small button flipped out, or maybe for a damaged camshaft.


Gilly

That does not sound too complicated. Perhaps I'll have a look tomorrow. If the culprit is that simple, I'll be pretty happy. Could the spacer you mentioned, or any other part, dislodge or otherwise move in a manner that causes damage? Also, how does a hydraulic compensator collapse?

Having never taken the valve cover off on my own, and not being familiar with what's underneath, I am a bit apprehensive. Still, I get the impression that there is nothing delicate or easily breakable under there.

I am also now wondering if this problem could be the root of my occasionally rough idle, which is now considerably more pronounced and continuous.

The spacer is the only part I can think of that could become dislodged. Well, at least become dislodged and cause the symptoms you have.
The lifter can collapse if it wears out internally or the check valve becomes worn or defective.

Gilly

OK. I'll have a look later today. Thanks.

The culprit was ...
 

The culprit was the first forward hydraulic lifter/compensator on the passenger side. Interestingly, this is the first failed lifter my mechanic has seen in his 40+ years of working on Mercedes.

This was also the first time I have seen the inside of my engine, and it is safe to say that given what I observed, replacing lifters & rocker arms, etc. is a quick DIY job. The only apparent gremlin would be removing the lifter from the rocker arm. My first impulse would have been to pry out the locking ring at the top of the lifter housing in the rocker arm, but the lifter is actually just tapped (or hammered) out through the bottom, and a new one slides in and snaps into place.

I have immediately noticed a very significant correction to the rough idle/stumbling problems that have plagued me for so long. There is still a very faint roughness, which I attribute to my fuel/air mixture needing adjustment (like a dope, I forgot to do it while I was there) and perhaps a dirty fuel filter. Power is a bit greater, since the “crippled” cylinder is now healed, and feels smoother and more torquey. Also, hot starts are more immediate.

Overall, a good, and very inexpensive repair. (I paid $75, parts and labor. If I did it myself, cost would have been about $10.00 for the lifter and 30-45 minutes to replace.)

Now, on to that darned idler Arm Bushing... :D